An electrically conductive buoyant cable is an electrical cable having a relative density below 1. The cable typically includes one or more conductors. Because the relative density of the electrically conductive buoyant cable is below 1, it will float on the surface of the water. In cases of interest in this application, the electrically conductive buoyant cable is connected to a mechanical device, which used for underwater applications, such as a pool cleaning device. The electrically conductive buoyant cable is used to provide an electrical power source to the pool cleaning device. Using the cable, it will be appreciated that a major part of the cable floats on the water. The remaining part of the cable runs between the cleaning device at the bottom of the water and the water surface.
The above described electrically conductive buoyant cable will not stay totally under the water. Remaining totally under water would hinder the normal performance of the cleaning device. For example, the cable could become entwined with the cleaning device preventing the device from moving along the pool surface.
As a result of the cable being buoyant, it will not rest upon the floor of the pool having water in it.
An additional advantage of the cable being buoyant is that it will not become entwined with obstacles on the floor of the pool while the pool has water in it. If a non-buoyant cable were used and rested at the bottom of the water, it would cause a great amount of tension to be exerted the cable. In fact, such a cable could reach its maximum value and break. Such breakage would cause the cable to cease to be able to perform its function.
Additionally, the electrically conductive buoyant cable must have a certain flexibility. Otherwise, the working area of the pool cleaning device will be greatly limited. Also, the moving speed and moving direction of the device will be affected. FIG. 1 shows the analysis of the forces exerted on the electrically conductive buoyant cable during work. During operation, the electrically conductive buoyant cable may be affected by torque, pressure and tension exerted by outside obstacles. In order to prevent these forces from damaging the electrically conductive buoyant cable, improvements are needed. They discover and use cable with smaller relative density, better flexibility and higher tension resistance capability.
FIG. 2 shows a sectional view of an electrically conductive buoyant cable of the prior art. A filler layer 21 is located between a jacket 22 and a fiber layer 23. There is also a filler layer 21 between the fiber layer 23 and the conductor 24. The filler layer has a relative density lower than 1. This is, in fact, how the electrically conductive buoyant cable has a relative density lower than 1 and is able to float on the water. The fiber layer 23 is made of fibers, which are used to withstand the tensile force exerted on the electrically conductive buoyant cable. The conductor 24 is a pair of the electrically conductive buoyant cables. The conductor 24 includes a pair of electrical wires, which are typically straight or twisted. The conductor 24 additionally contains water-proof and insulating material for good protection.
FIG. 2 shows other examples of known electrically conductive buoyant cables. As described below, there are typically three types of known cables.
In one example, a soft hollow tube encloses the conductor. Thus, with the same mass, the volume of the electrically conductive buoyant cable increases. Therefore, it has increased buoyancy. However, the hollow part of this kind of electrically conductive buoyant cable does not contain any components to withstand pressure. The electrically conductive buoyant cable will deform once there is sufficient outside pressure. This deformation leads to a decrease in the volume of the cable and thus causing the cable to lose buoyancy. Also, the jacket 22 and the filler layer 21 of this buoyant cable example are made of different materials. Using different materials increases the likelihood that there will be layer separation.
In this example, the electrically conductive buoyant cable will easily deform when it is subjected to certain types of torque. Once the cable starts to deform, all the deformation will focus on the part, which deforms the earliest. As a result, the electrically conductive buoyant cable will fold itself and irreversibly deform. Furthermore, using a cable of this construction increases the likelihood that water will leak into the soft hollow tube damaging all or part of the cable. Such leakage will consequently lead to loss of buoyancy of the entire cable.
In this example of the buoyant cable, the soft hollow tube and the conductor enclosed in the tube are separate. When the electrically conductive buoyant cable is subject to a tensioning force, the force received by the tube and the conductor will be different. The reaction of each element is therefore also different. So, there will likely be layer separation and the cable causing the cable to become irreversibly deformed after the tensioning force.
In another example of the electrically conductive buoyant cable, foaming plastic or rubber material is used to surround the conductor. Such material is used to increase the buoyancy of the buoyant cable. The use of foaming plastic or rubber material with air pockets to increase buoyancy typically lowers the tensile resistance the cable. In normal operation, the cable will be subjected to a higher tension force during the extension and withdrawal actions of placement and removal of the pool cleaning device from the pool, respectively.
When in use, the cable must withstand pressure when deep under water. In these situations, the cable may collapse and deform because of its cable construction having a foaming material. The cable may therefore become damaged when deep under water. There also exists here the problem of layer separation in this example as well.
In the next example of the electrically conductive buoyant cable, the plastic material is mixed with micro-spheres and is wrapped around the coaxial cable. Plastic or other insulating material of low relative density is used to make the jacket of this electrically conductive buoyant cable. This cable has a better buoyancy capability and higher tension resistance capability. However, fusion is not possible between the plastic and the micro-spheres. The junction between them can only withstand limited ripping force. If that limit is exceeded, there will likely be layer separation.
Additionally, in this example, there is a saturation point where further increase quantity of micro-spheres is not possible. Generally, known technology makes it difficult to have more than 40% by volume of micro-spheres embedded in plastic material. One drawback of this construction is that the diameter of the cable as well as the thickness of the buoyant material is increased. Additionally, the flexibility of the cable, especially its ability to bend is reduced. The micro-spheres are embedded in the jacket of the cable, which is made of the plastic or insulating material. Furthermore, the construction consistent with the above, weakens the physical properties of the cable jacket. Such weakening may cause the jacket to be unable to resist abrasion and become torn.
The electrically conductive buoyant cables mentioned above consists of a multi-layers structure, made from different materials. During the manufacturing process, it is needed to compress several times in order to finish the production of an entire cable. This leads to higher than necessary manufacturing costs.
The invention of the buoyant tether cable (the U.S. Pat. No. 4,110,554) relates to another multi-layered buoyant tether cable. FIG. 3 shows the sectional view of the buoyant tether cable of the invention. The buoyant tether cable consists of a circular jacket (31) and a center stress core (32) has a plurality of stress bearing elements (3221) contained within a core tape binder (321). There are three pairs of conductor elements including a first pair (33), a second pair (34) and a third pair (35) and additional conductor element (36). All the above elements twine around the central stress core. The three pairs of conductor elements (33), (34) and (35) can be identical.
The center stress core (32) has six stress bearing elements (322) contained within a core tape binder (321). Six stress bearing elements (322) are cabled around a central core element (322) in a six around one configuration. The central core element (322) is arranged on the longitudinal axis of the entire buoyant tether cable. Each stress-bearing element is preferably composed of three-stress bearing members twisted among themselves which are, in turn, contained within a jacket (321). This arrangement provides a tension bearing capability to the buoyant tether cable.
The conductor core (332) of each conductor element in each of the pairs of conductor elements (33), (34) and (35), can be a hollow low density, high strength plastic for increased buoyancy. Cabled around the conductor element core (332) are five insulated, twisted pairs of conductive wires (334). The conductor core (332) and the five conductive wires (334) are enclosed by the low-density, high strength plastic-like conductor tape binder (331).
The circular jacket (31) circumferentially surrounds the plurality of conductor elements which are cabled around the center stress core (32). Accordingly, interstices (37) are formed between the center stress core (32) with the conductor elements (33), (34), (35) and (36) and the outer circular jacket (31). Interstices (37) are substantially filled with a quantity of micro-spheres in a silicone oil medium, so as to increase the buoyancy of the buoyant tether cable.
In the interstices (37) nearer to the circular jacket (31) are seven interstitial stress members (38). Each interstitial stress member (38) contains at least two stress-bearing members (382) twisted between or among themselves and cabled within the interstices (37) and enclosed in a jacket (381) of a high strength, low density plastic-like material similar to the circular jackets (3221).
This buoyant tether cable contains a honeycomb structure. The buoyancy of the cable is increased. The pressure and tension resistance capability is also increased. The cable will not easily deform. However, the flexibility of this buoyant tether cable is poor. The cable consists of a multi-layered structure, which is made of different materials. Also, micro-spheres are added into the filler layer. Once the buoyant tether cable is being twisted, it will not be able to withstand the torque. The cable will be damaged and deformed, and the problem of layer separation may easily happen. Since the structure of this cable is rather complicated, the manufacturing procedure will be complicated and the manufacturing cost will also be high.
The invention of the floating cable (Chinese patent CN01279396) relates to a floating cable. FIG. 4 shows a sectional view of this new floating cable. The floating cable includes a coaxial wire (40), twisted wires (41) and a silk rope (42). They are enclosed by a frothy polyethylene (43). The frothy polyethylene (43) is enclosed by a light and heat resisting polyethylene protection layer (44). The coaxial wire (40) is made of the high-tension resistance copper core layer (404), the low density insulating polyethylene layer (403), the high-tension resistance copper cover layer (402) and the light and heat resisting polyethylene protection layer (401). The order of the components are arranged from inside to outside, which means the copper wire layer is the inner layer while the protection layer is the outer layer. The twisted wires (41) consists of high-tension resistance copper core layer (414) at the inside and the low density insulating polyethylene layer at the outside (413). Their outer layers consist of polyester cover (412) at the inside and light and heat resisting polyethylene protection layer (411) at the outside.
This floating cable consists of a multi-layered structure and different layers are made of different materials. There are infusible materials located far away from the central axis of the floating cable. When the cable is twisted or bent, fusion cannot occur between the two neighboring layers of different materials. The polyester cover layer (412) cannot fuse with the neighboring light and heat resisting polyethylene protection layer (411). The low density insulating polyethylene layer (413) cannot fuse with the neighboring polyester cover layer (412). The low density insulating polyethylene layer (413) cannot fuse with the neighboring high-tension resistance copper core layer (414). The high-tension resistance copper cover layer (402) cannot fuse with the neighboring light and heat resisting polyethylene protection layer (401). The low density insulating polyethylene layer (403) cannot fuse with the neighboring high-tension resistance copper cover layer (402). The high-tension resistance copper core layer (404) cannot fuse with the neighboring low density insulating polyethylene layer (403). The silk rope (42) cannot fuse with the neighboring frothy polyethylene layer (43). This leads to the phenomenon of layer separation. Moreover, the manufacturing procedures will be complicated and the manufacturing cost will be high due to the multi-layered structure of the floating cable.
The prior art while useful has been shown to have certain defects during applications. Improvements are therefore needed.